Many conventional electronic devices, such as small handheld devices, desktop and notebook computers, mobile handsets, PDA and digital music players, have an input mechanism for navigating a cursor or maneuvering a graphical user interface (GUI) function on such a device. By far, the most popular choice of navigation mechanism for input devices is the optical navigation system. In general, an optical input device tracks the relative movement between a navigation surface, such as a mouse pad or a work surface, and an image sensor within the optical input device. Light is illuminated towards the navigation surface or a target object by a light source such as a light emitting diode. Images of the illuminated navigation surface or multiple frames of digital image data of the illuminated target object are captured by a sensor and subsequently processed and further translated as a cursor movement on the input device.
More recently, the optical finger navigation system has been widely adopted in many handheld portable devices to provide navigation function by simply moving a finger on a finger interface surface of such portable device. The operational concept of such an optical finger navigation system is quite similar to a conventional optical mouse with the sensor for such finger navigation system is generally positioned facing up from the device. And in contrast to the tracking on a working surface with a typical mouse, the tracking surface of the optical finger navigation system is a user's finger. The navigation system translates the finger movement to a motion of a cursor or a navigation function on the screen of the portable device. While an optical finger navigation system can be effective, such systems are still prone to erroneous cursor movements caused by sunlight or other unwanted ambient light striking the sensor.
Another known limitation in many finger navigation devices is the unintended cursor movement when a finger is initially placed on the finger interface surface or as it is being lifted off the finger interface surface. The placing and lifting of a finger can cause unintended cursor jittering or a sudden jump of the cursor. In addition, such erroneous cursor movement is more obvious when the speed of the finger movements is high.